I've used Gmail since 2004, and now I have about 3000 Gmail contacts. I don't recognize the vast majority of them and many of my contacts are just email addresses. Over the years I've synced my contacts with every social network and cloud sync service out there and now my address book is a real mess. I only use my address book for personal mail. I have less than 200 people that I actually keep in touch with - I don't exactly know how the other 2800 contacts got there. I sync my Gmail with iCloud, so my iPhone's contact list is a mess too.

Is there some technique, application or service to magically clean up my address book? Perhaps I could delete everyone who I have not sent any email to.

All you have to do is start your free account and auto-import from gmail (and other platforms). Most of the duplicates will be auto-merged during this import process. No data is lost during this. Then, starting at that point, simply check the checkbox next to the ones you wish to delete and click the delete button. If the auto-merge missed any duplicates, just select those contacts and choose 'manual merge'.

At this point, you now have a clean, duplicate free address book online. You can then export your address book (or just a subset of it) in gmail format. Before you upload it to gmail, I would first delete ALL of your existing google contacts. Then upload the CSV that was exported from conXt.

I tried conXt yesterday, after finding your description and apparently not much else on the market. Some quick feedback: really like the intelligent merge features, as well as the manual merge. The relaxed approach to fields, multiple entries is great. A few things could be better: Right now it's only only keyboard/mouse usable. Could do with better smartphone integration (app for Android?). And if not, then at least the website should work with smartphone/tablet format. If you're still developing it, is there a place to leave detailed feedback on features / bugs?
– Assad EbrahimJun 2 '13 at 9:25